JPH0732379A - Manufacture of biodegradable resin foam - Google Patents

Abstract

PURPOSE:To provide a technique for obtaining foam of biodegradable resin and molding it in a suitable shape. CONSTITUTION:Moisture and biodegradable resin 10 are substantially cast in a cylindrical vessel, raised at its temperature to the vicinity of a softening point or a melting point to be fluidized in a heated and pressurized state while the resin 10 is forcibly fed, and its fluidized resin of the heated and pressurized state is injected in an atomized state from a narrow opening 12 of the vessel in permeable molds A. Biodegradable resin particles of the atomized state are charged in corners of the molds A to be foamed, the foamed cells are not collapsed, and uniform foam as shaped in the molds is obtained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a foam of a biodegradable resin which has been spotlighted in place of synthetic resin.

[0002]

2. Description of the Related Art Generally, ordinary synthetic resins are used in a wide variety of fields because they are excellent in mass productivity, moldability, and durability. Among them, synthetic resin foams are lightweight and have a buffer property. Due to its high price, it is used as a protective case for fragile objects such as glassware, as a cushioning material for packing transported goods, as a food and drink container, as well as as a heat insulating material and soundproofing material. However, since the amount of synthetic resin products to be discarded has become huge, various problems have been raised.

That is, when a synthetic resin is incinerated, a large amount of harmful gas is generated to pollute the atmosphere, and when it is discarded as it is, oxidation and photodecomposition do not occur, so that its shape is maintained for many years, and the environment is maintained. To contaminate. Further, since the synthetic resin has a very strong intermolecular bonding force, when it is incinerated, it generates high heat and shortens the service life of the furnace wall.

For these reasons, biodegradable resins have recently attracted attention and have been actively developed. This biodegradable resin is, for example, one containing a starch-based polymer and is decomposed by microorganisms in the soil or water, and therefore is very effective as a waste countermeasure.

Regarding the processing technology of the biodegradable resin, the processing technology of the film material is currently being put to practical use, but if foaming can also be realized, its application will be greatly expanded, and the advantages of the biodegradable resin will be further enhanced. Can be utilized. Examples of the technique for foaming the resin include a method of charging styrene beads into a molding die, adding steam and then depressurizing to obtain a group of expanded beads, and an extruder such as an organic solvent of styrene resin. There is known a method in which the resin is added together with the foaming agent, and the resin is foamed by a depressurizing action when the resin is extruded.

[0006]

However, since the biodegradable resin has different properties from ordinary synthetic resins, there are various problems. One of the problems is that the biodegradable resin starts foaming as soon as it is released from the pressurized state, but the viscosity is high when the biodegradable resin is heated and becomes fluid. Therefore, it is difficult for the biodegradable resin to enter the inside of the mold, and as a result, part of the biodegradable resin is extruded from the cylinder and foams before reaching the inner surface of the mold, resulting in a corner of the mold. In the parts and intricate parts, the part that should reach the inner part and should be foamed foams in the middle and collects in front of it, forming a void in the inner part, and in this state, the extruded biodegradable resin is forward. The foamed part of is pressed from the back side, and this part is crushed. Thus, if the portion is crushed from the rear side even if it is once foamed, a foam having a desired shape cannot be obtained, and a foam having sufficient cushioning performance cannot be obtained.

The present invention has been made under such circumstances, and an object thereof is to suppress collapse of foam cells of a biodegradable resin and to obtain a uniform foam having a desired shape. It is to provide a method for producing a biodegradable resin foam.

[0008]

According to the present invention, while substantially inserting water and a biodegradable resin into a cylindrical container having a stenosis opening at the front, and pushing the biodegradable resin to the stenosis opening. The fluid is heated and pressurized to form a fluid under heating and pressurization, and the fluid under heating and pressurization is injected from the constriction opening into the air-permeable mold in an atomized state and biodegradable in the atomized state. It is characterized in that resin particles are foamed and molded into a shape corresponding to a molding die.

[0009]

The biodegradable resin is heated to, for example, the softening point or the melting point while being pushed into the constriction opening to become a fluid under heating and pressurization, and the water present at the same time has a boiling point under pressurization. As a result, the fluidized biodegradable resin is trapped inside the biodegradable resin without evaporating. When this fluidized material in the heated and pressurized state is injected from the narrowed opening into the air-permeable molding die in an atomized state, the biodegradable resin particles in the atomized state spread to every corner of the molding die and are heated and pressurized. The water that was suddenly released from the mold was expanded and expanded in an attempt to evaporate at once, and the evaporated water was dissipated outside the breathable mold, while the atomized biodegradable resin It foams and collects, and a foam having a desired shape and homogeneous can be obtained without crushing the foam cells.

[0010]

EXAMPLES Examples of the present invention will be described below.
Before describing a specific manufacturing method, the biodegradable resin will be described first. A biodegradable resin means a resin material whose physical properties are deteriorated based on a biological action.There are two types: a type in which the resin itself is completely decomposed and a type in which a resin that is difficult to decompose is blended to provide disintegration. is there. The former type includes products produced by microorganisms, products using natural polymers, products produced from petroleum-based raw materials, and the latter type includes blends with starch and blends with aliphatic polyesters. Etc. These biodegradation mechanisms include various modes such as decomposition by enzymes such as lipase, amylase, cellulase, and protease, decomposition by microorganisms such as activated sludge, and decomposition by soil in natural environments such as forests and cultivated lands.

More specifically, polyhydroxybutyric acid and its derivatives, pullulan, cellulose-chitosan mixture,
Examples thereof include esterified products of cellulose, amylose and wood flour, polyester-nylon copolymers, polyester copolymers, blends of starch and polyethylene, polyvinyl alcohol, polyether, polyurethane and polyamide. These generally have low melting points and are accelerated in the presence of water.

In this embodiment, the biodegradable resin used was Mater-Bi "Matterby" (registered trademark) pellets sold by Nippon Synthetic Chemical Industry Co., Ltd.
This is a NO belonging to the Montedison Group in Italy
In connection with the development of VAMONT, it is considered to be a thermoplastic biodegradable polymer in which derivative products from multiple agricultural products such as starch and denatured polyvinyl alcohol infiltrate into each other at the molecular level and are bonded by hydrogen bonds. It is what Further, it is said that biodegradation is promoted by absorbing water and swelling, and exhibits biodegradability equivalent to that of paper in an environment in which microorganisms survive.

Further, in order to put the biodegradable resin and the water into a cylindrical container described later, an appropriate amount of water may be contained in advance when molding the biodegradable resin pellet for foaming. Alternatively, for example, a pretreatment step of positively containing water in the biodegradable resin granules may be provided. Further, water itself may be added directly into the hopper together with the biodegradable resin, or may be supplied into the cylinder through a kneader, as long as the biodegradable resin and water are substantially supplied. .

Further, if a hygroscopic fine particle substance which has absorbed moisture in advance, such as talc (talc) or silica, is added to the biodegradable resin, the fine particle substance has water compatibility and dispersibility with the resin. Since it is higher than that of direct addition, and the water content in the fine particles can be foamed starting from the fine particles at the time of foaming, as a result, a finely and uniformly foamed product can be obtained.

Next, a manufacturing apparatus used in the embodiment of the present invention will be described with reference to FIG. 1. Reference numeral 1 is a cylinder corresponding to a cylindrical container, and a hopper 11 for charging a molding material is provided above a rear end portion thereof. It is provided. A nozzle 12 having a narrowed opening at the tip is formed at the tip of the cylinder 1, and a heater 13 for heating is arranged around the cylinder 1.

Inside the cylinder 1, a screw 2 extending in the front-rear direction is arranged close to the inner wall thereof, and the rear end of the screw 2 extends rearward from the rear end opening of the cylinder 1. , Is connected to a hydraulic motor 21 for rotating the screw 2. Further, a piston 23 slidably arranged in the injection cylinder 22 is attached to the rear part of the hydraulic motor 21, and therefore the piston 23, the hydraulic motor 21 and the screw 2 are integrally moved by the hydraulic pressure in the front-rear direction. At the same time, the screw 2 is rotated by the hydraulic motor 21.

A so-called in-line screw type injection molding machine is constructed in this way, and a breathable molding die A is arranged at the tip of this molding machine. This molding die A is provided with a nozzle 12 via a stationary die set 7. Of the fixed side mold 3 in which the cavity 31 communicating with the opening (narrowing opening) is formed, and the movable side mold 4 in which the core 41 is formed. In this embodiment, the cavity 31 has, for example, a square shape, and the core 41 has, for example, a shape having a small square convex portion on one surface of the square shape. A foamed product having a shape corresponding to A can be obtained.

The mold A is provided with a mold clamping mechanism in combination, and the mold clamping mechanism guides the movable side mold 4 so as to contact and separate the movable side mold 4 while facing the fixed side mold 3, for example. , 43 and an operating mechanism 44 for moving the movable side mold 4 into and out of contact with each other.

Here, the diameter of the nozzle 12 is such that the fluid material in the heated and pressurized state is atomized from the nozzle 12 into the cavity 31.
In order to inject into the molding space formed by the core 41 and the core 41, it is necessary to make the diameter smaller than that of the nozzle of the conventional general injection molding machine. That is, the diameter of the nozzle of the conventional general injection molding machine is set to, for example, 2 to 5 mm, but in this embodiment, for example, the diameter of the nozzle 12 is set to a small diameter of about 1 mm.

The molding die A is made of a porous material having an infinite number of network-like pores that communicate the inside and the outside almost all over. As the porous material, there are foamed metal, sintered materials such as metal or ceramics sintered by adding a filler capable of forming voids, metal wire, punching metal, etc. Can be used, and as a simple structure, a single punched metal formed into a predetermined shape can also be used.
Here, if the pores of the porous material are large, the steam discharge efficiency and the ventilation efficiency are good, but if they are too large, the surface of the molded body after foaming becomes strongly uneven due to the pores and the surface becomes rough. Therefore, the size of the pores of the porous material is set within a range in which the smoothness of the surface according to the use of the molded article is obtained, and the range in which the ventilation resistance does not become too large. One using punching metal can be mentioned because it is easy to set and has a simple structure.

The manufacturing method of the present invention will be described using the manufacturing apparatus configured as described above. First, the mold A is clamped, and the biodegradable resin granules 10 are fed into the hopper 11. As shown in FIG. 2A, the inside of the cylinder 1 is pushed forward by the screw 2. Granules of biodegradable resin 1
0 is heated to a temperature around the softening point or the melting point due to the shearing force accompanying the rotation of the screw 2 and the heating from the inner wall of the cylinder 1 by the heater 13 while being pushed, It collects as a fluid in the internal space. At this time, the internal space is heated and pressurized, and the water contained in the granules 10 of the biodegradable resin is trapped in the fluidized material without evaporating from the fluidized material.

Then, as shown in FIG. 2B, the rotation of the screw 2 is stopped and the piston 2 in the injection cylinder 22 is stopped.
3 is operated to move the screw 2 forward, and the fluid material is injected from the nozzle 12 into the molding space formed by the cavity 31 and the core 41 in the molding die A in an atomized state.

In order to inject in the atomized state, the nozzle 12 has a smaller diameter than the conventional one as described above, and the injection speed of the fluid material by the screw 2 and the fluid material The pressure difference before and after the extrusion may be adjusted appropriately. It should be noted that the nozzle 12 required to make the atomized state
Since the diameter of the above varies depending on the extrusion speed of the fluid material, it is not limited to about 1 mm as described above.

On the other hand, since the outside of the mold A is open to the atmosphere, the cavity 31 of the mold A is also at atmospheric pressure through the porous portion of the mold A. Therefore, the biodegradable resin that has been rapidly injected into the cavity 31 in the atomized state is rapidly exposed to the atmospheric pressure from the heating and pressurizing state, and the water trapped in this is instantaneously evaporated. Foam. The force of expansion of the water vapor works in the biodegradable resin, but the outermost portion of the biodegradable resin is in contact with the molding die A, so that the shapes of the cavity 31 and the core 41 are restricted. Then, the water vapor is diffused to the outside through the porous portion of the mold A, while foaming is performed for each particle inside the biodegradable resin to form a bubble 100 (foam cell), and these particles are entangled with each other. A foamed body B of biodegradable resin in which the whole is shaped into one by fusion bonding is obtained.

Next, as shown in FIG. 2 (c), when the screw 2 is rotated and retracted, the fluidized biodegradable resin begins to collect in the internal space of the cylinder 1 on the tip side of the screw 2 again. Prepare for the next shot.
During this time, in the cavity 31 in the molding die A, the cooling and solidification of the biodegradable resin foam after molding is completed, so the molding die A
The mold is opened, the foam B is taken out, the mold is clamped again, and the following operation is performed.

In the above method, since the fluid biodegradable resin is ejected from the nozzle 12 into the cavity 31 under the atmospheric pressure in the atomized state, the atomized biodegradable resin particles form the cavity 31. While being filled up in every corner of the molding space formed by the core 41, the biodegradable resin particles in each atomized state foam and aggregate. Therefore, since the foaming is completed with the biodegradable resin entering every corner of the mold A, even if the mold A has a complicated shape, the foam cells are accumulated in the position floating from the inner surface of the mold and It is possible to mitigate or avoid the problem that the biodegradable resin is forced to be pressed and crushed, and therefore it is possible to suppress the crushing of the foam cells that have once foamed, so that a uniform foam with a desired shape can be obtained. As a result, sufficient cushioning performance can be obtained.

In the present invention, a ventilation atmosphere may be provided outside the molding die A. In this case, since water vapor is forcibly released to the outside of the molding die A, the water content after vaporizing and expanding and contributing to foaming is increased. There is an advantage that the contraction caused by the redeposition of the can be suppressed.

The molding die A may be placed inside the decompression chamber to reduce the pressure of the atmosphere outside the molding die A to atmospheric pressure or less. In this case, a large pressure difference can be obtained. At the same time, the action of forced release of water vapor is further increased, and dew condensation on the mold A is suppressed.

In the present invention, the number of nozzles 12 is not limited to one, and a plurality of nozzles 12 may be provided, for example, as shown in FIG. 3. In some cases, a large number of nozzles 12 may be provided at the tip of the cylinder 1 as shown in FIG. You may provide the shower part 15 provided with the minute injection hole 14 of this. Furthermore, although not shown, a runner,
When biodegradable resin is introduced into the mold via the gate, reduce the diameter of the runner and gate so that the biodegradable resin is introduced into the mold in an atomized state. You can do this.

Further, in the present invention, as shown in FIG. 5, a decompression chamber 5 divided into a plurality of airtight decompression chambers 51 to 53 is provided so as to surround the molding die A, and decompression pipes corresponding to the respective chambers are provided. 61 to 65 are provided and the degree of decompression by each decompression pipe is changed so that the filling state is adjusted so that the biodegradable resin particles in the atomized state are efficiently and sequentially filled from the back of the molding space. You may
In this case, the decompression chamber 5 is configured so that it can be opened and closed at the same time as the molding die A, for example. Here, the nozzle of the injection molding machine is open, and the hopper on the raw material supply side of the cylinder is also open, and although a certain degree of tightness is secured by the raw material and the molten resin, the airtightness inside the cylinder is If the pressure is low, pressurization will be insufficient, and due to the balance between the softening point or melting point of the biodegradable resin and the boiling point of water under pressure, some water may vaporize in the cylinder before injection, causing foaming. In addition, foaming may occur from the nozzle in the dripping state. Therefore, in the present invention, it is preferable to improve the hermeticity by providing the nozzle with a valve, sealing the hopper on the side of the raw material supply section, and further attaching a rotary valve to the raw material supply port. Alternatively, for example, polyethylene glycol or the like may be dissolved in water as a solute, and this water may be added, whereby the boiling point of water may be raised and foaming in the cylinder before injection may be suppressed.

The biodegradable resin foam obtained by the present invention is not limited to the use as a cushioning material, but may be used as a heat insulating material, a soundproofing material or the like.

[0032]

As described above, according to the present invention, a biodegradable resin can be uniformly foamed and can be molded into an appropriate shape, and it can be used as a substitute for a conventional synthetic resin foam. This can contribute to the reduction of environmental pollution such as garbage pollution.

[Brief description of drawings]

FIG. 1 is a schematic vertical sectional view showing an example of a manufacturing apparatus used in an embodiment of the method of the present invention.

FIG. 2 is a schematic vertical cross-sectional view showing how an embodiment of the method of the present invention is carried out using an inline screw type injection molding machine.

FIG. 3 is a schematic perspective view of a cylinder tip portion provided with a plurality of nozzles.

FIG. 4 is a schematic perspective view of a cylinder tip portion provided with a shower portion.

FIG. 5 is a schematic vertical sectional view showing a main part of another manufacturing apparatus for carrying out the method of the present invention.

[Explanation of symbols]

 A Mold B Foam 1 Cylinder 11 Hopper 12 Nozzle 2 Screw 23 Piston 3 Fixed Side Mold 31 Cavity 4 Movable Side Mold 41 Core 5 Decompression Chamber 51, 52, 53 Decompression Chamber

Claims (1)

[Claims] 1. A water container and a biodegradable resin are substantially put into a cylindrical container having a constriction opening in the front, and the biodegradable resin is heated and pressurized while being pushed to the constriction opening. The fluidized material in the state of heat and pressure is injected from the constriction opening into the air-permeable molding die in the atomized state to foam the biodegradable resin particles in the atomized state, A method for producing a biodegradable resin foam, which comprises molding the biodegradable resin foam into a shape according to the above.